Timeline - Summary of Events
January 2010 – Health Department Investigation Begins
On January 7, Vermont Yankee Nuclear Power Station notified the Vermont Department of Health that samples taken in November 2009 from a ground water monitoring well (identified as GZ-3) on site contained tritium. This finding signaled an unintended release of radioactive material, and meant that other radioisotopes may have contaminated the environment.
On January 11 Vermont Yankee, with assistance from the Nuclear Regulatory Commission (NRC), began its own investigation to identify sources of the tritium and magnitude of the contamination.
February 2010 – Major Source of Leak is Found
On February 14, the major source of the leak was found. A pair of stream pipes in the Advance Off-Gas (AOG) pipe tunnel were found to be badly corroded and leaking nuclear steam. The floor drain of this concrete tunnel was found to be clogged with construction debris and mud, which caused condensate from the steam pipes to pool inside the tunnel and leak out at a failed joint.
May 2010 – Plume of Contamination Defined, New Leak Detected
On May 14, soil testing in the area around the leak had measured concentrations of radioisotopes consistent with a leak of nuclear reactor water. Steadily decreasing tritium concentrations in samples taken from the ground water monitoring wells drilled since January showed the movement of tritium contamination in the ground water generally west to east into the Connecticut River.
On May 29, Vermont Yankee officials notified the Health Department that a new leak was identified and stopped at the AOG drain line. This occurred as the AOG system was being started up after its refueling outage.
June 2010 - 2012 – Ongoing Investigation
Since the leak was first reported, the Health Department closely monitored and reported on the investigation. Investigation summary reports are available up until 2012.
2010 Vermont Yankee Surveillance Report - This describes the amount and types of radiation found on and near the Vermont Yankee Nuclear Power Station.